Heat treatment of metal



Aug. 23, 1955 R. M. WICK ET AL HEAT TREATMENT OF METAL Filed 00%,. 11, 1949 United ttes Patent Ofiice 2,716,079 Patented Aug. 23, 1955 HEAT TREATMENT OF METAL Richard M. Wick, Allentown, and Stewart H. Jones and Samuel W. McClemens, Johnstown, Pa., assignors to Bethlehem Steel Company, a corporation of Pennsyl- Vania Application (Ectober 11, 1949, Serial No. 120,635

Claims. (Cl. 148-40) This invention relates to improvements in methods of heat treatment of metal. It relates in particular to the electrical heat treatment of metal, and specifically to the continuous treatment, such as annealing or patenting, of wire or similar material. By means of the resistance of the material to the passage of an electric heating current therethrough, the wire or other material is heated by passing such a current therethrough continuously as it is advanced at uniform speed past spaced contacts through which such current is supplied to the material under treatment.

In the specific embodiment of our invention which has resulted in the advantages hereinafter pointed out, the current is supplied through contacts of molten metal. While the use of such molten metal contacts or electrodes is already known in the art, their use as heretofore practiced has involved certain undesirable features which it is one purpose of our invention to eliminate.

In the electrical heat treatment of wire or similar material, using molten metal contacts, as heretofore practiced, the usual arrangement in a system using two contacts has been to pass the wire from the pay-off reels first through a contact pot which is at the operating voltage, and then to quench the wire in a second contact pot which was grounded so that electrical interference with subsequent processing operations was avoided.

The fact that the first contact pot was at operating voltage meant that the wire and reel equipment, etc., feeding into this pot was also at an elevated voltage. This required somewhat elaborate safety precautions to prevent accidents. Should the wires feeding into the system contact each other, a short circuit would occur that would have as its least consequence the interruption of proper heat treatment. Should the wire or equipment be grounded, more serious consequences would ensue. There existed the constant danger that individuals operating the equipment might accidentally come in contact with the advancing wire, resulting possibly in serious injury.

Furthermore, in the prior practice, the advancing wire reached an elevated temperature between the two contact pots, being quenched at a reduced temperature in the second pot. This condition of course tended to raise the temperature of the molten metal in the quench pot. In order to prevent the temperature of the metal in the quench pot from rising above the desired point, it was necessary to cool the pot in some way, to dissipate the heat constantly being supplied to it by the incoming highly heated wire. This practice of course resulted in the wastage of a substantial amount of heat.

It is a particular object of our invention to effect economy in the operation of the method by conserving some of the heat which, in the practice of prior known methods, has been wasted.

It is a further object of our invention to make practicable a method of the type here involved which will be safe to practice and will eliminate certain dangerous features of the heretofore known methods.

The foregoing and other objects of our invention and the means by which we accomplish them will be clearly understood from the following description and claims, together with the drawings, in which Fig. 1 is a diagrammatic representation in elevation of the apparatus and its arrangement used in the practice of our invention.

Fig. 2 is a partially sectional view in elevation of the second contact pot which is at operating voltage; and

Fig. 3 is a partially sectional view in elevation of the first contact pot which is also the quench pot.

Referring now to the drawings, there is shown feed-in reel 10 from which a plurality of wires 11 to be treated are led into the first contact pot 12 in which there is maintained a bath of molten metal, such as lead, 13. Contact pot 12 which, as will be explained, is also the quench pot, is at ground potential. Sinkers 14 serve to keep incoming wires 11 well beneath the surface of the molten metal and below the level of the outgoing wires hereinafter described. From contact pot 12 wires 11 travel horizontally as far as driven capstan 15, at which point the direction of travel of wires 11 is reversed. This driven capstan is of benefit to the operation through its action of tension relief, without which inferior metallurgical properties are obtained in the wire being heat treated. The capstan is made of a heat resistant, dielectric material and is insulated from the ground. The capstan is made effective by either synchronous speed or over-drive involving a small amount of slippage, usually between 5 and 10%. From capstan 15, wires 11 travel over sheave 16 and downwardly into second contact pot 17, which is at operating potential. Sinkers 18 hold the wires beneath the surface of molten metal 19 in contact pct 17. The sinkers 18 are controllable, being pneumatically actuated by remote control, and serve to raise the wire out of the lead to disconnect the wire from the electrical circuit. This is useful in operation where changes are being made in remote parts of subsequent processing steps. From contact pot 17, the wires travel back to pot 12, traveling through guide structure 20. Guide structure 20 which is made of di-electric material contains a plurality of paths to accommodate the number of wires being heated and to keep them out of contact with each other during this stage of treatment. During this stage of their travel the wires are heated up by the current to the desired temperature of treatment. Upon entering contact pot 12, wires 11 are quenched in the molten metal 13 to the temperature thereof, and thereafter leave pot 12, and are wound on take-up reel 21. Wires 11, upon entering pot 12 from the feed-in reel and upon leaving pot 12 after being quenched, are at ground potential.

The molten metal in contact pots 12 and 17 is connected by electric cables 22 and 23 to a source of supply (not shown) of a current of electricity which is subject to automatic voltage control. The operational control involves setting the wire voltage by adjustment to the correct wire temperature determined by pyrometric observation at a point just before entry into the grounded contact pot 12.

Referring now particularly to the matter of thermal economy, it is readily apparent that upon quenching the heated wires in pot 12, from a temperature of say, 1650 F. to 1100 B, there is given up to the molten metal in pot 12, 550 in temperature. In the prior practice, since this would result in overheating of the molten metal, it was necessary to provide means for dissipating, and thus wasting this excess heat. In our method, the heat equivalent of the loss of temperature in the highly heated wire is recovered by the preheating of the cold wire being fed into the system from the feed-in reel. Ob-

viously this results in a saving, as less heat will then be required to bring the incoming wire up to treatment temperature.

As has been hereinbefore pointed out, the wires both entering and leaving the system are at ground potential, thus eliminating the hazard to operating personnel that was constantly present when the wire entering the system, and the reel equipment, etc., were at a high voltage.

The temperature of the molten metal in contact pots 12 and 17 will vary, depending on the nature of the material under treatment. Thus, for example, in the patenting of high carbon wire the metal in pot 12 will be maintained at a temperature within the range of about 900 F. to about 1150 F. In the course of its treatment, the wire will be electrically heated to about 1650 F., from which temperature it is quenched in pot 12 at the end of the treatment. In the annealing of wire, the treatment temperature will be about 1350 F., from which temperature the wire will be quenched in pot 12. As has been hereinbefore pointed out, this temperature loss in the heated wire is recovered by preheating the wire being fed into the system.

The temperature of the molten metal in contact pot 17 is determined in accordance with the requirements of the operation. Generally this temperature is about the temperature of the wire entering the pot, and if the lead temperature is slightly low causing lead dragout, this can be prevented by increasing the lead temperature.

In addition to the above mentioned advantages of heat economy and greater safety, our method has resulted in greater flexibility of operation, better and more uniform quality of products and greater speed in operation.

Because of the tension control afforded by the intermediate driven capstan a wider range of wire sizes can be heat treated by this method than heretofore, without changing the physical arrangement, e. g., the distance through which the wire is electrically heated. This improvement is important in operations. For example, it was found possible, without changing any distances involved to electrically patent wire of 0.30 diameter at one extreme and 0.028" diameter at the other end. It is believed that wire of both larger and smaller sizes can be successfully treated by our method.

Greater uniformity and quality of heat treated product is obtained because of several factors. Uniform low tension assists in obtaining uniform temperature through improving uniformity of cross section, especially at very elevated temperatures. More uniform and constant quench temperatures improve the constancy of the metallurgical properties developed. Evidence observed points out that the intermediate contact pot operating on electrically pre-heated wire promotes greater uniformity of power input to the wire, and therefore improves the constancy of product quality. personal safety in operation, the elimination of wire voltage above ground potentials at the reels, for example,

Besides the improvement to 5;

avoids the short circuit possibility thereby and thus increases product uniformity. The grounding of the wire before the input pot has eliminated previously experienced accidents which, when they sometimes occurred seriously impaired the metallurgical quality of the wire.

We claim:

1. In a method of continuously heat treating metal v passing said wire past said first molten metal contact, said first molten metal contact being at ground potential and said second molten metal contact being at operating potential.

2. A method of continuously patenting high carbon steel wire by electrical resistance heating thereof comprising passing said wire through a first contact of molten metal which is at a temperature of approximately 900 F. to 1150 F., further heating said wire by electrical resistance and passing the wire through a second contact of molten metal which is at a temperature approximately the temperature of the heated wire, continuing the electrical resistance heating of said wire until the wire is heated to a temperature of approximately 1650 F., and finally quenching said wire by passing it through said first contact of molten metal, said first contact being maintained at ground potential and said second contact being maintained at operating potential.

3. A method of continuously annealing steel wire by electrical resistance heating thereof comprising passing said wire through a first contact of molten metal which is at a temperature of approximately 1100 F further heating said wire by electrical resistance and passing the wire through a second contact of molten metal which is at a temperature slightly in excess of the temperature of the heated wire, continuing the electrical resistance heating of said wire until the wire is heated to a temperature of approximately 1350 F., and finally quenching said wire by passing it through said first contact of molten metal, said first contact being maintained at ground potential and said second contact being maintained at operating potential.

4. A method of continuously heat treating metal wire or the like by passing a heating current of electricity therethrough which comprises passing said wire past a first molten metal contact in one direction, then reversing the direction of travel of said wire by passing it around a driven capstan which is rotating at a speed at least as great as the speed of travel of said wire, thereafter passing said wire past a second molten metal contact and then again passing said wire past said first molten metal contact, said first molten metal contact being at ground potential and said second molten metal contact being at operating potential.

5. A method of continuously heat treating steel wire or the like by electrical resistance heating thereof comprising passing said wire through a first contact of molten metal which is at ground potential, then heating said wire by electrical resistance, passing said wire through a second contact of molten metal which is at operating potential, continuing the electrical resistance heating of said wire until it has reached the desired temperature and then quenching said heated wire by passing it through said first contact of molten metal, whereby the heat given up by said heated wire in being quenched is recovered by the wire first passing through the said first contact of molten metal and preheats said incoming wire.

References Cited in the file of this patent UNITED STATES PATENTS 1,285,887 Alexander et al Nov. 26, 1918 1,386,645 Moore Aug. 9, 1921 1,916,407 Bellis July 4, 1933 2,304,225 Wood et al. Dec. 8, 1942 OTHER REFERENCES Transactions: The Electrochemical Society, vol. 84, 1943, pages 270-272. 

1. IN A METHOD OF CONTINUOUSLY HEAT TREATING METAL WIRE OR THE LIKE BY PASSING A HEATING CURRENT OF ELECTRICITY THERETHROUGH, THE STEPS COMPRISING PASSING SAID WIRE PAST A FIRST MOLTEN METAL CONTACT, THEREAFTER PASSING SAID WIRE PAST A SECOND MOLTEN METAL CONTACT AND THEN AGAIN PASSING SAID WIRE PAST SAID FIRST MOLTEN METAL CONTACT, SAID FIRST MOLTEN METAL CONTACT BEING AT GROUND POTENTIAL AND SAID SECOND MOLTEN METAL CONTACT BEING AT OPERATING POTENTIAL. 